Sensing switch and detecting method using the same

ABSTRACT

Provided are a sensing switch and a sensing method using the same. The sensing switch includes: a substrate; a supporter on the substrate; a sensing plate that is connected to a side of the supporter and is in parallel with the substrate by a predetermined distance; a receptor binding region on an upper surface of an end portion of the sensing plate; an electric or magnetic field generation device that induces deflection of the sensing plate when a receptor bound to the receptor binding region is selectively bound to an electrically or magnetically active ligand; and a pair of switching electrodes that are separated by a predetermined distance and is connected when the sensing plate contacts the substrate due to the deflection of the sensing plate. A target material need not be labelled, a signal processing of a fluorescent or electrical detection signal using an analysis apparatus is not required, and a signal can be directly decoded by confirming whether a current flows through the switch.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 12/272,183, filed on Nov. 17, 2008 , now U.S. Pat. No. 7,790,440which is a divisional application of U.S. application Ser. No.11/347,185, filed on Feb. 3, 2006 now U.S. Pat. No. 7,510,865, whichclaims the benefit of Korean Patent Application Nos. 10-2005-0010987filed on Feb. 5, 2005, and 10-2005-0092668 filed on Oct. 1, 2005, in theKorean Intellectual Property Office, the disclosures of which areincorporated herein in their entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for sensing a biomoleculeor a chemical material, and more particularly, to a sensing switch thatphysically moves due to an electrostatic force between an electrodehaving the same polarity as a ligand and another electrode having theopposite polarity to the ligand or due to a magnetic force between amagnetic bead bound to a ligand and a magnetic field generation device,thus acting as a switch, and a sensing method using the same.

2. Description of the Related Art

Effective sensing of biomolecules and chemical materials is required ina wide range of applications, such as biochips. A biochip is formed byimmobilizing a receptor (biomolecules), such as DNA or a protein, withhigh density on a support, and can be used to analyze gene expressioncharacteristics, gene defects, protein distribution, reactioncharacteristics, and the like. Biochips are categorized into microarraychips and lab-on-a-chips according to where a receptor is affixed. Amicroarray chip is formed by affixing a receptor to a solid support, anda lab-on-a-chip is formed by affixing a receptor to a microchannel. Inorder to find a target material in a sample able to bind to a receptorimmobilized on a support, the biochip requires a system that can detectwhether a receptor immobilized on a support.

In general, a DNA chip for gene analysis is used to analyze a gene bylabeling a sample DNA with a fluorescent pigment, reacting the labeledsample DNA with a receptor on the chip, and detecting the fluorescentmaterial remaining on the surface of the chip using a confocalmicroscope and a CCD camera (See U.S. Pat. No. 6,141,086). However, itis difficult to miniaturize the equipment required for such an opticalsensing method and the result cannot be digitally output. Therefore,much research has been conducted to develop a new method in which theanalysis result can be output via an electrical signal.

A method of and apparatuses for electrochemically detecting DNAhybridization using a metal compound, which can be easily oxidized andreduced, has been researched in many labs including a Clinical MicroSensor (See U.S. Pat. Nos. 6,096,273 and 6,090,933). In this case, whenDNA is hybridized, another compound containing a metal that can beeasily oxidized and reduced is combined with the hybridized DNA to forma complex, which is electrochemically detected [Anal. Chem., Vol. 70,pp. 4670-4677, 1998; J. Am. Chem. Soc., Vol. 119, pp. 9861-9870, 1997;Analytica Chimica Acta, Vol. 286, pp. 219-224, 1994; and BioconjugateChem., Vol. 8, pp. 906-913, 1997.] However, the electrochemical methodsalso require a labeling process.

In addition, a conventional fluorescent or electrochemical sensingmethod requires a sensor, a measuring apparatus for measuring the outputof the sensor, and an analysis device for processing a signal obtainedfrom the measuring apparatus. Therefore, the entire system is bulky,many expensive apparatuses are required, and skilled engineers arerequired to perform each operation. Even when all these requirements arecomplied with, it takes a long time to obtain a final result and a noiseis guaranteed in connections between apparatuses.

In order to overcome these problems, the inventors of the presentinvention confirmed that a sensor can physically moves due to anelectrostatic force between an electrode having the same polarity as aligand and another electrode having an opposite polarity to the ligandor due to a magnetic force between a magnetic bead bound to a ligand anda magnetic field generation device, thus acting as a switch, so that aminiaturized sensing switch that needs not require signal processing canbe manufactured.

SUMMARY OF THE INVENTION

The present invention provides a sensing switch that can performmechanical sensing and electrical switching at the same time and doesnot require signal processing after the sensing.

The present invention also provides a sensing circuit including aplurality of sensing switches that are connected in the form of a logiccircuit.

The present invention also provides a method of sensing whether a ligandis bound using the sensing switch.

According to an aspect of the present invention, there is provided asensing switch including: a substrate; a supporter on the substrate; asensing plate that is connected to a side of the supporter and is inparallel with the substrate by a predetermined distance; a receptorbinding region on an upper surface of an end portion of the sensingplate; an electric or magnetic field generation device that inducesdeflection of the sensing plate when a receptor bound to the receptorbinding region is selectively bound to an electrically or magneticallyactive ligand; and a pair of switching electrodes that are separated bya predetermined distance and is connected when the sensing platecontacts the substrate due to the deflection of the sensing plate.

According to another aspect of the present invention, there is provideda sensing switch including: a substrate; a supporter on the substrate; asensing plate that is connected to a side of the supporter and is inparallel with the substrate by a predetermined distance; a receptorbinding region on an upper surface of an end portion of the sensingplate; a push-out electrode that has the same polarity as a ligand abovethe sensing plate; a pull-in electrode that has the opposite polarity tothe ligand below the sensing plate; and a pair of switching electrodesthat are separated by a predetermined distance and is connected when thesensing plate contacts the substrate due to respective repulsive andattractive forces of the push-out electrode and the pull-in electrode.

According to still another aspect of the present invention, there isprovided a sensing switch including: a substrate; a supporter on thesubstrate; a sensing plate that is connected to a side of the supporterand is in parallel with the substrate by a predetermined distance; areceptor binding region on an upper surface of an end portion of thesensing plate; a magnetic bead that is selectively bound to a receptorbound to the receptor binding region through a ligand; a magnetic fieldgeneration device below the sensing plate; and a pair of switchingelectrodes that are separated by a predetermined distance and isconnected when the sensing plate contacts the substrate due to amagnetic field generated by the magnetic field generation device.

The sensing plate may be a cantilever or seesaw-type lever (like aseesaw), and preferably, the seesaw-type lever. When the sensing plateis the seesaw-type lever, the sensing plate may extend in oppositedirections from the center of a connecting beam which connects twosupports formed on the substrate, and is in parallel with the substrateby a predetermined distance, and two receptor binding regions can beformed on upper surfaces of arms of the sensing switch. The arms of thesensing plate move up and down in the same manner as a seesaw, thusconnecting and separating the switching electrodes that are separatedfrom each other by a predetermined distance.

The supporter may support the connecting beam or the sensing plate thatis in parallel with the substrate by a predetermined distance and mayact as a pivot for rotation of the connecting beam.

The sensing plate may be composed of a material such that the sensingplate can be easily bent by the respective repulsive and attractiveforces of the push-out electrode and the pull-in electrode. Therefore,the entire sensing plate or at least a portion of the sensing platecontacting the switching electrode may be composed of an electricalconducting material so that the switching electrodes on the substratecan be connected to each other when the sensing plate is bent downward.

The connecting beam may be narrower and thinner than the sensing plate,and thus can be easily bent by the respective repulsive and attractiveforces of the push-out electrode and the pull-in electrode. Theconnecting beam may be integrated with or separated from the sensingplate.

The ligand may be a biomolecule or chemical material, which iselectrically charged. For example, the ligand may be a nucleotide, aprotein, a peptide, an antibody, an antigen, or a liquid or vapourchemical material, which may be selectively bound to the receptor.

The ligand can be directly bound to the receptor binding region.Alternatively, a receptor that can be bound to a ligand can be bound tothe receptor binding region. In the latter case, the receptor can be anyreceptor that can bond to the ligand, and may be DNA, RNA, peptidenucleic acid (PNA), locked nucleic acid (LNA), a protein, a peptide, ora chemical material. In the present specification, the term ‘thebinding’ indicates a specific binding, such as hybridisation of anucleic acid and Ag-Ab interaction.

The receptor binding region may be made of any material to which abiomolecule or a chemical material can bond. For example, the receptorbinding region may be made of a material selected from glass, metal,plastic, and silicon. In addition, the surface of the receptor bindingregion can be modified to have —COOH, —SH, —OH, a silane group, an aminegroup, or an epoxy group using a conventional biochip surfacemodification method so as to allow the receptor or the ligand to bebound.

A ligand that is to be selectively bound to a receptor, or a secondaryreceptor that is to be selectively bound to the ligand may be adhered tothe magnetic bead.

The receptor may be immobilized on one of two receptor binding regions.Preferably, different ligands are respectively immobilized on the tworeceptor binding regions. In this case, one of two ligands may act as areference receptor and thus differential detection can be performed anda background signal can be effectively removed.

According to another aspect of the present invention, there is provideda sensing circuit that forms ‘AND’ and/or ‘OR’ logic circuits byarranging a plurality of sensing switches according to the presentinvention in series and/or parallel.

In the ‘AND’ logic circuit, at least two sensing switches are connectedin series. In this case, a current flows only when all of the switchesare closed. In the ‘OR’ logic circuit, at least two sensing switches areconnected in parallel. In this case, a current flows only when at leastone of the switches is closed. In the present invention, various logiccircuits can be formed by combining the plurality of ‘AND’ and/or ‘OR’logic circuits.

The sensing circuit may performs sensing and analyzing at the same timein response to output signals from the ‘and/or’ logic circuits. Thesensing circuit may have at least one input line and at least one outputline. The sensing and analyzing of a plurality of receptors can beperformed at the same time by applying a current to the input line andmeasuring the current from each output line. In addition, the signalprocessing is not required after the signal sensing. That is, thebinding of the different receptors in sensing switches forming a circuitcan be effectively analyzed by only confirming whether a current isoutput from the output line, for example, whether a lamp is on or off,without processing the sensed signal.

According to yet another aspect of the present invention, there isprovided a method of sensing ligand binding, the method including:providing a ligand to a receptor binding region of the sensing switch;binding the ligand, and a receptor immobilized on the receptor bindingregion; applying a voltage that has the same polarity as the ligand to apush-out electrode and a voltage that has an opposite polarity to theligand to a pull-in electrode; raising and lowering the sensing plate inresponse to the respective repulsive and attractive forces between thepush-out electrode and the pull-in electrode and the ligand so that thepair of switching electrodes are connected or separated; and sensingwhether a current flows between the switching electrodes.

According to another aspect of the present invention, there is provideda method of sensing ligand binding, the method including: adhering amagnetic bead to a ligand that is to be selectively bound to a receptoror a secondary receptor that is to be selectively bound to the ligand;providing to the receptor binding region of the sensing switch theligand or secondary receptor adhered to the magnetic bead; adhering themagnetic bead to the receptor binding region by selectively binding theligand and the receptor; removing the ligand or second receptor adheredto a magnetic bead that is not bound to the receptor binding region;generating an electric field by using an electric field generationdevice below the sensing plate; raising and lowering the sensing platein response to the generated magnetic field so that the pair ofswitching electrodes are connected or separated; and sensing whether acurrent flows between the switching electrodes.

A receptor may be immobilized on only one of two receptor bindingregions of the sensing switch. Preferably, different ligands may berespectively immobilized on two receptor binding regions such thatdifferential binding of the different ligands can be sensed. In thiscase, the two receptor binding regions move like a seesaw such that anend of a sensing plate to which more receptors are bound descends. Atthis time, one of two kinds of ligands acts as a reference receptor, andthus a background signal can be effectively removed.

In a conventional electrical sensing method, resistance, impedance, theamount of a current, and the like are measured using a measuringapparatus and then signal processing is performed. On the other hand,according to the present invention, the binding of a receptor can beeasily identified by confirming whether a current flows through asensing switch or not, for example, by confirming whether a lamp is onor off.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is a front view of a sensing switch (cantilever) according to anembodiment of the present invention;

FIG. 2 is an exploded perspective view of a sensing switch (cantilever)according to another embodiment of the present invention;

FIG. 3A is a front view of a sensing switch (seesaw-type lever)according to another embodiment of the present invention;

FIG. 3B illustrates an operation of the switch when sensed;

FIG. 3C is a perspective view of a sensing switch according to anotherembodiment of the present invention;

FIG. 4A is a schematic view when the sensing switch shown in FIG. 3A isclosed;

FIG. 4B is a schematic view when the sensing switch shown in FIG. 3A isopen;

FIG. 5A is a schematic view of a conventional DNA chip detection system;

FIG. 5B is a schematic view of a DNA chip detection system according toan embodiment of the present invention;

FIG. 6A is a schematic diagram of a conventional differential sensingsystem;

FIG. 6B is a perspective view of a differential sensing system accordingto an embodiment of the present invention;

FIGS. 7A and 7B illustrate the analysis results obtained using theconventional differential sensing system shown in FIG. 6A;

FIG. 8A illustrates an ‘AND’ logic sensing circuit according to anembodiment of the present invention;

FIG. 8B illustrates an ‘OR’ logic sensing circuit according to anembodiment of the present invention;

FIG. 8C illustrates a combined circuit including at least one ‘AND’logic circuit and at least one ‘OR’ logic circuit;

FIGS. 9A and 9B illustrate scales for measuring the torque of thesensing switch shown in FIG. 3;

FIG. 10 is a schematic view of an apparatus that is used to simulate asensing switch according to an embodiment of the present invention;

FIGS. 11A and 11B illustrate the results of a simulation of the sensingswitch according to an embodiment of the present invention;

FIG. 12 is a graph of a magnetic force with respect to a distancebetween a magnetic bead and a magnetic field generation device of thesensing switch shown in FIG. 2;

FIG. 13A illustrates a scale of a sensing plate that is used in asimulation of the sensing switch shown in FIG. 2;

FIGS. 13B and 13C illustrates the result of a simulation performed usingthe sensing plate shown in FIG. 13A;

FIG. 14 schematically illustrates a method of manufacturing the sensingswitch shown in FIG. 2;

FIGS. 15A and 15B are magnified scanning electron microscopy (SEM)images of a sensing switch manufactured using the method illustrated inFIG. 14; and

FIG. 16 shows sensing results indicating that the sensing switch shownin FIG. 15 effectively senses a receptor.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described more fully with reference tothe accompanying drawings.

FIG. 1 is a front view of a sensing switch (cantilever) according to anembodiment of the present invention. Referring to FIG. 1, the sensingswitch includes a substrate 1, a supporter 2 formed on the substrate 1,a sensing plate 4 that is connected to a side of the supporter 2 and isin parallel with the substrate 1 by a predetermined interval, a receptorbinding region 5 formed on an upper surface of the sensing plate 4, apush-out electrode 6 that has the same polarity as a ligand and disposedabove the sensing plate 4, a pull-in electrode that has the oppositepolarity to the ligand and disposed below the sensing plate 4, and apair of switching electrodes 9 that are separated by a predeterminedinterval and can be connected to each other when the sensing plate 4contacts the substrate 1 due to a repulsive force and an attractiveforce of the push-out electrode 6 and the pull-in electrode 8.

In FIG. 1, to the receptor binding region 5, a ligand able to bond witha receptor can be directly immobilized. When the ligand is directly orindirectly immobilized on the receptor binding region 5, a repulsiveforce occurs between the ligand and the push-out electrode 6 because thetarget molecule and the push-out electrode 6 have the same polarity andan attractive force occurs between the ligand and the pull-in electrode8 because the ligand and the pull-in electrode 8 have oppositepolarities, and thus the sensing plate 4 is bent downward. At this time,an end of the sensing plate 4 contacts the switching electrodes 9 andthus a current flows.

Although the switching electrodes 9 are illustrated as a single unit inFIG. 1, they are separated by a predetermined distance. Thus, before thesensing plate 4 contacts the switching electrodes 9, the current doesnot flow.

FIG. 2 is an exploded perspective view of a sensing switch (cantilever)according to another embodiment of the present invention. Referring toFIG. 2, the sensing switch includes a substrate 1; a supporter 2 on thesubstrate 1; a sensing plate 4 that is connected to a side of thesupporter 2 and is in parallel with the substrate 1 by a predetermineddistance; a receptor binding region 5 on an upper surface of an endportion of the sensing plate 4; a magnetic bead 10 that is selectivelybound to a receptor 12 bound to the receptor binding region 5 through aligand 11; a magnetic field generation device 13 below the sensing plate4; and a pair of switching electrodes 9 and 9′ that are separated by apredetermined distance and is connected when the sensing plate 4contacts the substrate 1 due to a magnetic field generated by themagnetic field generation device 13.

In FIG. 2, the receptor 12 is immobilized on the receptor binding region5, the magnetic bead 10 is bound to the ligand 11, and the magnetic bead10 is bound to the receptor binding region 5 on the upper surface of anend of the sensing plate 4 through selective binding between the ligand11 and the receptor 12. The magnetic bead 10 bound to the receptorbinding region 5 moves toward the substrate 1 due to a magnetic fieldgenerated by the magnetic field generation device 13 and thereby, thesensing plate 4 bends.

The magnetic bead may be in a form of suspension, and can be obtainedfrom, for example, Dynal AS Inc. The magnetic bead may include aferromagnetic bead, a paramagnetic bead, and a super-paramagentic bead.The magnetic bead can be prepared using a method disclosed in EP No.0106873.

FIG. 3A is a front view of a sensing switch (seesaw-type lever)according to another embodiment of the present invention, and FIG. 3Billustrates an operation of the switch shown in FIG. 3A when sensed.Referring to FIGS. 3A and 3B, the sensing switch includes a substrate 1,two supporters 2 and 2′, a connecting beam 3 connecting the supporters 2and 2′, a sensing plate 4 that crosses the center of the connecting beam3 and is in parallel with the substrate 1 by a predetermined distance,receptor binding regions 5 and 5′ formed on upper surfaces of two armsof the sensing plate 4, a push-out electrode 6 that has the samepolarity as the ligand and disposed above the sensing plate 4, pull-inelectrodes 7 and 7′ that have opposite polarities to the ligand and aredisposed below the sensing plate 4, and a pair of switching electrodes(not shown) that are separated by a predetermined interval and can beconnected to each other when the sensing plate 4 contacts the substrate1 due to a repulsive force and an attractive force of the push-outelectrode 6 and the pull-in electrodes 7 and 7′.

Referring to FIG. 3A, different receptors, such as oligonucleotide, arerespectively immobilized on the receptor binding regions 5 and 5′, andmore target DNA molecules are immobilized on the receptor binding region5 than the receptor binding region 5′. As a result, the receptor bindingregion 5 is more negatively charged than the receptor binding region 5′.The push-out electrode 6 disposed above the sensing plate 4 is an anodewith the same polarity as that of DNA, and the pull-in electrodes 7 and7′ disposed below the sensing plate 4 are cathodes with the oppositepolarity to that of DNA. The pull-in electrodes 7 and 7′ can be separateor integrated. In FIG. 3B, since the receptor binding region 5 exhibitsa greater negative charge than the receptor binding region 5′, thesensing plate 4 is inclined due to effective electrostatic forcesbetween the negative push-out electrode 6 and the positive pull-inelectrode 7, that is, a repulsive force and attractive force, thushaving a seesaw motion.

FIG. 3C is a perspective view of a sensing switch according to anotherembodiment of the present invention. Referring to FIG. 2C, detaileddescriptions of the receptor binding regions 5 and 5′ formed on theupper surfaces of the two arms of the sensing plate 4, the push-outelectrode 6 disposed above the sensing plate 4, the pull-in electrodes 7and 7′ disposed below the sensing plate 4, and the switching electrodesdisposed on the substrate 1 are not illustrated.

FIG. 4A is a schematic view when the sensing switch shown in FIG. 3Aclosed, and FIG. 4B is a schematic view when the sensing switch shown inFIG. 3A is open. Referring to FIGS. 4A and 4B, when the switch isclosed, the current flows between switching electrodes on the substrate;and when the switch is open, the current does not flow between theswitching electrodes on the substrate. Accordingly, the sensing switchcan act as a sensor and a switch at the same time. In other words, whenthe ligand is immobilized on the receptor binding regions 5 and 5′, theelectric charge on the receptor binding regions 5 and 5′ is changed andthe switch is closed. As described above, since the sensing switchaccording to an embodiment of the present invention can be closed oropen, a logic circuit, such as a common electric circuit, can bemanufactured.

Since the sensing switch can perform mechanical sensing and electricalswitching at the same time, a signal processing subsequent to thesensing is not required. In addition, the sensing switch requiresminimal circuitry and power, and thus it can be more miniaturized than aconventional apparatus performing sensing and signal processing switch.Further, the sensing switch produces minimal circuit noise, such asflicker and white noise, and the noise can be minimized by eliminating aconnection noise between a sensor and a post processor since a postprocessor is not required.

FIG. 5A is a schematic view of a conventional DNA chip detection system,and FIG. 5B is a schematic view of a DNA chip detection system accordingto an embodiment of the present invention. Referring to FIG. 5A, whenspots A, B, and C on a DNA chip are scanned and a signal is processedusing an analysis apparatus, the spots A, B, and C exhibit an intensitygreater than a predetermined level. As a result, whether a targetpatient is a MODY patient can be identified. However, referring to FIG.5B, according to an embodiment of the present invention, three sensingswitches on a single DNA chip perform sensing and analysing and whethera final output line is closed is confirmed using a simple apparatus,such as a lamp. As a result, whether a target patient is a MODY patientcan be identified.

FIG. 6A is a schematic diagram of a conventional differential sensingsystem, and FIG. 6B is a perspective view of a differential sensingsystem according to an embodiment of the present invention. Thedifferential sensing system decreases a low common noisefactor/background noise, and thus decreases a high S/N ratio. Aconventional differential sensing system includes an analysis sensor anda reference spot/sensor (identical) as shown in FIG. 6A, and the resultsoutput by the sensors are analyzed using an analytical tool/electricalcircuit. Therefore, the conventional differential sensing systemrequires at least two identical spot/sensor, and differentialamplification/post analysis of an acquired signal. On the other hand,referring to FIG. 6B, the differential sensing system according to anembodiment of the present invention can be miniaturized, consume minimalpower, and obtain a high S/N ratio or less noise and predominantly highsensitivity, because a single sensing switch can perform functions ofmore than one conventional apparatus.

FIGS. 7A and 7B illustrate the analysis results obtained using theconventional differential sensing system shown in FIG. 6A. Referring toFIG. 7A illustrating a conventional method, in order to differentiallysense the spots A, B, and C of the DNA chip, each of the spots A, B, andC is scanned and then the intensity of each spot is compensated bysubtracting the intensity of the background spot B therefrom. As aresult, differential intensities of the spot A and the spot C can beobtained. On the other hand, referring to FIG. 7B illustrating a sensingmethod according to an embodiment of the present invention, a singlesensing switch compares the amounts of the receptors immobilized on thespot A and the spot C disposed on arms of a sensing plate by operatingas a seesaw operates, so that the differential sensing of the spot A andthe spot C can be directly performed without any production of a commonnoise due to spot B.

FIG. 8A illustrates an ‘AND’ logic circuit of a sensing circuitaccording to an embodiment of the present invention, and FIG. 8Billustrates an ‘OR’ logic circuit of a sensing circuit according to anembodiment of the present invention. In the ‘AND’ logic circuitillustrated in FIG. 8A, when sensing switches 1 and 2 are turned on, forexample, when the subject is infected by HP2 and HP3, the output of thecircuit is activated. In the ‘OR’ logic circuit illustrated in FIG. 7B,when the sensing switch 1 closed or the sensing switch 2 closed, forexample, when the subject is infected by HP2 or HP3, the output of thecircuit is activated.

FIG. 8C illustrates a combined circuit including at least one ‘AND’logic circuit and at least one ‘OR’ logic circuit according to anembodiment of the present invention. HP2 and/or HP3 infection can beprecisely sensed by measuring on (1) or off (2) at outputs 1 and 2. Theresults diagnosed from the output signals of FIG. 8C are shown in table1.

TABLE 1 Output HP2 HP3 Output 1 Output 2 Infection Infection 1 1 ◯ ◯

0 1 ◯ X 1 0 X ◯ 0 0 X X

The highly sensitive sensing logic circuit according to an embodiment ofthe present invention is a landmark design for a LOC and may replace aconventional device sensor (DNA chip)+Scanner/controller+analysis tool(PC).

As for a working principle for the sensing switch, four torques, eachgiven byTorque=Force×distance,affect the sensing plate. The four torques are:

1) an electrostatic or magnetic torque (Me) that derives the movement ofthe sensing plate and depends on the arrangement and geometry ofelectrodes or a magnetic field generation device, an electric ormagnetic field, and the charge of a receptor, or a magnetic bead;

2) an inertial torque (I) that is proportional to angular accelerationand depends on the rotational inertia (I) of a rotating connecting beam;

3) a damping torque (D) that is proportional to a rotational speed anddepends on a damping factor (F), such as medium's viscosity or sensordimension; and.

4) a mechanical restoring torque (Mm) that is proportional to a tiltingangle and depends on a material composing the sensor andgeometry/design.

The relationship among the four torques can be given by

$\begin{matrix}{{{I\frac{\mathbb{d}^{2}\theta}{\mathbb{d}t^{2}}} + {F\frac{\mathbb{d}\theta}{\mathbb{d}t}} + {{Mm}(\theta)}} = {{Me}(\theta)}} & (1)\end{matrix}$

FIGS. 9A and 9B illustrate scales for measuring the torque of a sensingswitch according to another embodiment of the present invention. Thereceptor binding region is 80×30 μm², the sensor is made of dopedpolysilicon, Young's modulus (E) for the sensor is 150 Gpa, Poissonratio (v)=0.22 (for example), relative dielectric constant of a buffer(∈_(b)) is 50, and an applied voltage is 10V. Accordingly, in a steadystate

$\begin{matrix}{{{{I\frac{\mathbb{d}^{2}\theta}{\mathbb{d}t^{2}}} + {F\frac{\mathbb{d}\theta}{\mathbb{d}t}} + {{Mm}(\theta)}} = {{Me}(\theta)}}{when}} & (1) \\{{\frac{\mathbb{d}\theta}{\mathbb{d}t} = {0\mspace{14mu}\frac{\mathbb{d}^{2}\theta}{\mathbb{d}t^{2}}}},} & (2)\end{matrix}$and therefore, Mm(θ)=Me(θ)  (3).

As described above, a design parameter/requirement can be obtained usingan analytical solution, and most of all, whether the sensing switch canoperate or not can be confirmed. In order to obtain a dynamic response,such as a response speed of the sensor or the like, the equation (I)must be solved without setting dθ/dt or d′θ/dt² to 0. However, theobtaining of the dynamical response is not important at a time whenfeasibility of the sensor is considered.

The mechanical restoring torque is given by

$\begin{matrix}{\mspace{79mu}{{{Mechanical}\mspace{14mu}{restoring}\mspace{14mu}{torque}} = {\left( \frac{2{KG}}{l} \right)\theta}}} & (4) \\{{{K\left( {{Stiffness}\mspace{14mu}{{coeff}.\mspace{14mu}{Of}}\mspace{14mu}{the}\mspace{14mu}{beam}} \right)} = {w\;{t^{3}\left\lbrack {\frac{1}{3} - {0.21\frac{t}{w}\left( {1 - \frac{t^{4}}{12w^{4}}} \right)}} \right\rbrack}}}\mspace{20mu}{where}} & (5) \\{\mspace{79mu}{{{G\left( {{elastic}\mspace{14mu}{modulus}\mspace{14mu}{of}\mspace{14mu}{beam}\mspace{14mu}{in}\mspace{14mu}{shear}} \right)} = \frac{E}{2\left( {l + v} \right)}}\mspace{20mu}{and}}} & (6)\end{matrix}$(See B. R. Hopkins, design analysis of shafts and beams 2nd edition).

As a result, K (Stiffness coeff. Of the beam) is 2.25×10⁻²⁴ m⁴, G(elastic modulus of the beam in shear) is 61.47×10⁹ N/m², and therestoring torque is 9.22×10⁻⁹ Nm.

The electrostatic torque is be given byMe(θ)=Fe×distance, where

$\begin{matrix}{{Fe} = {{qE} = \frac{q\; V}{S\; ɛ_{b}}}} & (7)\end{matrix}$

The present invention will be described in detail with reference to thefollowing Examples. These examples are for illustrative purposes onlyand should not be construed as limiting the scope of the presentinvention.

EXAMPLE 1

Torque was measured using the sensing switch illustrated in FIGS. 9A and9B under the following condition: 80% non-specific binding to mismatchedreceptor (single mismatch receptor, hypothetically); immobilized 25 merreceptor DNA density of 2×10¹² molecules/cm²; 100% hybridization withperfect matched DNA (25 mer); a receptor of 5′SH-C6-AGATCAGTGCGTCTGTACTAGCACA 3′ (See A. Peterson, the effect ofsurface receptor density on DNA hybridization, Nucleic Acid Research2001, 29, 24, pp 5163-5168).

The results of steady state analysis are described below.

Total effective charge (q)=reactive surface area×molecules/area×numberof electrons/molecule×charge/electron=6×10⁻¹¹ C;

the electric field=10V/(50×10 um)=2×10⁵ N/C; and

Fe=1.2×10⁻⁵ N.

Accordingly, as described below, the sensor did not operate because theelectrostatic torque, was smaller than the mechanical restoring torque.

Electrostatic Torque=Fe×40 μm=4.8×10⁻¹⁰ Nm

Restoring torque=9.22×10⁻⁹ Nm

Some design/experimental tweaking was made in Example 1 and thefollowing different results were obtained.

First, in a first alteration, the applied voltage was 200V.

Electrostatic torque=9.6×10⁻⁹ Nm>9.22×10⁻⁹ Nm (Restoring torque).

Electrodes including an oxide insulting layer were assumed to interrupthydrolysis. In theory, the voltage can be increased to a dielectricbreakdown voltage (Oxide>10 MV/cm, liquid of about 1 MV/cm). In thepresent embodiment, the dielectric break down voltage of the liquid wasabout 1000V/10 um. The increase in the voltage resulted in theelectrostatic torque being greater than the mechanical restoring torque,and thus the switch operated.

In a second alteration, effective charges were increased using RCA.Hence, 100 times rolling multiplication (few minutes) and theelectrostatic torque (48×10⁻⁹ Nm) was larger than the mechanicalrestoring torque (9.22×10⁻⁹ Nm)

Electrostatic Torque=48×10⁻⁹ Nm>9.22×10⁻⁹ Nm (Restoring torque)

In a third alteration, beam designs and materials were modified. In thiscase, a lower young's modulus and a longer beam length was used. As aresult, the mechanical restoring torque was smaller than theelectrostatic torque and thus the switch was able to operate.

EXAMPLE 2

In order to confirm whether the sensing switch shown in FIG. 10 can actas a switch, a simulation experiment was conducted in which a nucleicacid used as biomolecule was sensed using the apparatus illustrated inFIG. 9. (See A. Peterson, the effect of surface receptor density on DNAhybridization, Nucleic Acid Research 2001, 29, 24, pp 5163-5168). ANSYS8.0 (obtained from ANSYS, Inc., USA) was used as a simulation program, ashell 93 (suited for large deflection) was used as an element, a beamwas made of gold, young's modulus was 75 GPa (silicon˜169 GPa),poisson's ratio was 0.42, a density was 1.932×10⁴ kg/m3 (silicon˜2.33e3kg/m3), the beam had a thickness of 1 μm, the relative permitivity of abuffer solution was 80, a gap between two electrodes was 100 μm, anapplied potential was 10 V, an immobilized 25 mer receptor DNA densitywas 2×10¹² molecules/cm², 100% hybridization with perfectly matched DNA(25 mer) was performed, and a receptor used was 5′SH-C6-AGATCAGTGCGTCTGTACTAGCACA 3′. Different designs as indicated inTable 2 were adopted. The simulation results are shown in FIGS. 11A(three beams) and 11B (six beams). (Etch hole was 5 μm×5 μm, Distancebetween holes: 5 μm). Referring to FIGS. 10A and 10B, the beam is bentenough to connect two electrodes in both cases, thus acting as a switch.

TABLE 2 # of beams beam length beam width square plate length deflection3  50 um 5 um 105 um  10 um 6 155 um 5 um 155 um 4.4 um

EXAMPLE 3

A force generated between the magnetic bead and the magnetic generationdevice that was sufficiently strong to move a switch but not greaterthan a binging force between the receptor and the ligand was measuredusing the sensing switch shown in FIG. 2

A BioMag® BM551 was used as the magnetic bead. Streptavidin as a ligandwas bound to the surface of the magnetic bead. A neodium magnet was usedas the magnetic field generation device. The magnetic bead and theneodium magnet had the following characteristics: Br=1.22 Tesla,μ₀=1.26×10⁻⁶ H/m, magnetic mass susceptibility=2.54×10⁻³ m³/kg,density=1.70×10³ kg/m³, magnetic susceptibility=4.31, beaddiameter=1.50×10⁻⁶ m, V=1.77×10⁻¹⁸ m³, and L_magnet=0.003 m.

The magnetic force with respect to the distance between the magneticbead and the magnetic filed generation device was measured using thevalues above and Formula 8.

$\begin{matrix}{{F_{mag} = {{\frac{V\;\chi_{m}}{\mu_{0}}\left( {\overset{\rightarrow}{B} \cdot \nabla} \right)\overset{\rightarrow}{B}} = {\frac{V\mspace{11mu}\chi_{m}}{2\mu_{0}}{\nabla\left( {\overset{\rightarrow}{B}}^{2} \right)}}}}{B_{x} = {\frac{B_{r}}{2}\left\lbrack {\frac{L + x}{\sqrt{R^{2} + \left( {L + x} \right)^{2}}} - \frac{x}{\sqrt{R^{2} + x^{2}}}} \right\rbrack}}} & (8)\end{matrix}$

The results are shown in FIG. 12. Referring to 12, the magnetic forcebetween the magnetic bead and the magnetic filed generation device was90 pN when they were separated by 1 mm.

Meanwhile, in general, the known mutual binding force betweenstreptavidin and biotin is 260±20 pN (See Proc. IEEE 85(4), 672-680,1997).

From the results, it was found that in the sensing switch according toan embodiment of the present invention, the magnetic force (90 pN)generated between the magnetic bead and the magnetic filed generationdevice was strong enough to move the sensing switch but smaller than abinding force (260±20 pN) of the receptor-ligand so as not to interruptthe binding between the receptor and the ligand.

EXAMPLE 4

A simulation was performed to determine that the sensing switch shown inFIG. 2 acted as a switch in the same manner as in Example 2. FIG. 13Aillustrates the dimensions of a sensing plate that is used in asimulation of the sensing switch shown in FIG. 2. The sensing plate wasformed of silicon single crystal (Young's modulus=169 GPa, Density=2330kg/m³) and had a thickness of 3 μm.

Under these conditions, the measured pressure was 0.1×90 N/m²=9 Pa.Under such a pressure, a distance between the sensing plate and theswitching electrode at which the sensing plate could be sufficientlybent to connect a pair of switching electrodes was measured. In thiscase, it was assumed that the magnetic bead was bound to 10% of thecross-sectional surface of the sensing plate. FIG. 13B shows the resultsof simulation.

From the results, the allowable distance between the sensing plate andthe switching electrodes was determined to be 180 μm or less. Withinthis range, the sensing plate was able to contact the switchingelectrodes when an electric field was applied.

In addition, it was determined whether the sensing plate bent due to theweight of the sensing plate and the magnetic bead such that the sensingplate contacted the switching electrodes even when an electric filed wasnot applied. In this case, it was assumed that the magnetic bead wasbound to the entire cross-sectional surface of the sensing plate. FIG.13C illustrates the results of the simulation.

From the results, it was determined that, when a magnetic field was notapplied, a distance required to maintain the separation of the sensingplate and the switching electrodes was 1.6 μm or greater.

That is, when the sensing plate was separated from the switchingelectrodes by 1.6-180 μm, the sensing switch could act as a switch.

EXAMPLE 5

The sensing switch according to an embodiment of the present inventionshown in FIG. 2 was manufactured using a semiconductor processingtechnique.

FIG. 14 schematically illustrates a method of manufacturing the sensingswitch shown in FIG. 2.

Referring to FIG. 14, in order to manufacture a sensing plate, first, anoxide layer 22 and a SOI wafer 23 were sequentially formed on a SOIwafer 21. The surface of the SOI wafer 21 was coated with a PR 24 andwas etched using a conventional method using a first mask (operation a).Then, the SOI wafer 23 located opposite to the SOI wafer 21 was coatedwith a PR 25 and etched using a conventional method using a second mask(operation b). Next, the exposed oxide layer 22 was etched toward theSOI wafer 23 to manufacture a sensing plate (operation c).

Then, an oxide layer 26 was coated with poly-Si 27 and etched using athird mask (operation d). The resulting structure was patterned using afourth mask, thus forming a pair of switching electrodes 29 and acontact pad connected to the switching electrodes 29 (operation e).

The resulting patterned structure was coupled with the sensing switch(operation f). The sensing switch illustrated in operation f of FIG. 14corresponds to the sensing switch of FIG. 2, and corresponding elementshave the same reference numerals in the operation f of FIG. 14 and FIG.2.

FIGS. 15A and 15B are magnified scanning electron microscopy (SEM)images of a sensing switch manufactured using the method illustrated inFIG. 14.

EXAMPLE 6

It was determined whether the sensing switch manufactured in Example 5acted as a sensor.

A BioMag® BM551 was used as a magnetic bead. Streptavidin was bound tothe surface of the magnetic bead. A neodium magnet was used as amagnetic field generation device. A direct current voltage of 1 V wasapplied to pair of switching electrodes.

Two experiments were performed: when biotin was immobilized on areceptor binding region on an upper surface of an end of the sensingplate; and when biotin was not immobilized.

The results are shown in FIG. 16. Referring to FIG. 16, it was foundthat when biotin was immobilized on the receptor binding region of thesensing plate and a magnetic filed was applied, a current flowed.However, when biotin was not immobilized on the receptor binding region,a current did not flow. That is, the sensing switch according to anembodiment of the present invention was effectively able to sense areceptor.

As described above, according to the present invention, a targetmaterial, such as a biomolecule or chemical material, does not need tobe labeled, signal processing for processing a fluorescent or electricdetection signal using an analysis apparatus to process a fluorescent orelectrical detection signal is not required, and a signal can bedirectly decoded by confirming whether a current flows according towhether a switch is opened or closed. That is, a sensing switchaccording to the present invention is more convenient than aconventional sensing switch because mechanical sensing and electricalswitching can be performed at the same time, while conventionally, afterthe sensing, an acquired signal must be processed. In addition, minimalcircuitry and power are required in the present invention, and thus thesensing switch can be miniaturized than conventional sensing methodsthat have been developed, that is, the sensing and signal processing. Inaddition, the sensing switch has minimal circuit noise, such as flickerand white noise, and the noise can be reduced by eliminating connectionnoise between a sensor and a post processor since a post processor isnot required.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. A sensing switch comprising: a substrate; a supporter on thesubstrate; a sensing plate that is connected to a side of the supporter,is disposed parallel to and separated a predetermined distance from thesubstrate, and has a receptor binding region on an upper surface of anend portion thereof; a push-out electrode that has the same polarity asa ligand and is disposed above the sensing plate; a pull-in electrodethat has the opposite polarity to the ligand and is disposed below thesensing plate; and a pair of switching electrodes that are separated bya predetermined distance and are connected when the sensing platecontacts the substrate due to respective repulsive and attractive forcesof the push-out electrode and the pull-in electrode.
 2. The sensingswitch of claim 1, wherein the ligand is a nucleotide, a protein,peptide, an antibody, an antigen, a polymer, or a liquid or vaporchemical agent, and is selectively bound to the receptor.
 3. The sensingswitch of claim 1, further comprising a connecting beam which connectstwo supporters formed on the substrate, wherein the sensing plateextends in opposite directions from the center of the connecting beamand is disposed parallel with and a predetermined distance from thesubstrate, and two receptor binding regions are formed on upper surfacesof two arms of the sensing plate.
 4. The sensing switch of claim 3,wherein different receptors are respectively immobilized on the receptorbinding regions.
 5. A sensing circuit, comprising a plurality of thesensing switches of claim 1 arranged in series and/or in parallel, thusforming an ‘AND’ and/or an ‘OR’ logic circuit.
 6. The sensing circuit ofclaim 5, performing sensing and analyzing at the same time in responseto an output signal from the ‘AND’ and/or ‘OR’ logic circuits.